The present invention relates to automatic electronic or "computer" flash systems. In particular, the present invention relates to an automatic correct exposure annunciator for use with automatic electronic flash systems.
Automatic electronic flash systems include a light producing means, generally a flash tube, which is actuated to illuminate a scene being photographed. A light sensing or exposure control circuit detects the scene illumination and actuates a light terminating or light quenching means when sufficient light has been produced to properly expose a light sensitive film of an associated camera.
There is need for an annunciator which will indicate to the photographer whether sufficient light has been produced to properly expose the film. In U.S. Pat. No. 3,706,911 by Dennis J. Wilwerding, a correct exposure annunciator circuit is described which includes a switch responsive to the operation of the light quenching means. The closure of this switch energizes the annunciator. A reset switch is used to turn off the annunciator.
Although the correct exposure annunciator circuit of the Wilwerding patent is generally satisfactory, it does have some shortcomings. In particular, it typically requires a relatively large number of additional components (12 to 15 components in many cases). This increases cost and affects reliability of the flash system.
In U.S. patent applications Ser. Nos. 603,565 by James R. Adams, Jr. and Dennis J. Wilwerding and 603,564 by James R. Adams, Jr., improved correct exposure annunciators are described. These applications were filed Aug. 11, 1975 and are assigned to the same assignee as the present application. The referenced patent applications reduce the number of components required for a correct exposure annunciator. This results in lower cost and higher reliability of the annunciator circuit.
Although the annunciators described in the referenced patent application are generally satisfactory, there remains a need for other correct exposure annunciator circuits. For example, a correct exposure annunciator which uses low cost components, which does not require a separate power supply, and which remains lit for a relatively long period of time before being automatically terminated is desirable.